Recently, in order to improve the performance of safety systems such as an airbag, the operations of some safety systems are controlled in accordance with the weight of an occupant seated on a vehicle seat. As a conventional device which measures the weight of a seated occupant, a device is proposed which includes a load sensor between a vehicle floor and a seating portion of a vehicle seat to measure the weight of an occupant based on the amount of deformation of the vehicle seat (refer to Patent Document 1, for example).